1. Field of the Invention
The invention relates in general to a memory and a manufacturing method thereof, and more particularly to a memory with an isolation wall separating two charge storage layers and a manufacturing method thereof.
2. Description of the Related Art
As portable electronic products become more and more popular, the demand for flash memories grows rapidly in the market. When applied to memories on a main board or small-size memory cards, nonvolatile storage provided by flash memories breaks the limit of conventional optical and magnetic storage. The flash memory is stable and has low energy consumption. Also, there is no need to move components in the device. Therefore, the flash memory is an ideal solution for the nonvolatile storage of programs and data in the portable electronic products.
The flash memories in the present market are substantially divided into two types, NOR type and NAND type. The NOR type flash memories are based on Not-OR logical structure, and the NAND type flash memories are based on Not-AND logical structure. Compared to the NAND type structure, the NOR type structure speeds up data reading and reduces the time for bit rewriting through the parallel configuration. However, the NAND type structure has smaller memory cells and individual blocks than the NOR type structure. Also, the NAND structure has low energy consumption when programming and is faster in programming and erasing. Besides, the memory cell array of the NAND structure has higher density, so that the memory capacity per square millimeter is increased.
As to the present nonvolatile nitride memory, a nitride layer for storing charges generates two bits when the memory is programming. However, when the portable electronic products become smaller and lighter, the volume of the memory has to be reduced accordingly. Therefore, the two bits storing in the nitride layer interfere with each other when the memory is programming. Second bit effect occurs when the memory reads the two bits. As a result, the reliability and practicability of the memory is decreased greatly.